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Tag: mantle plumes

Super-computer modeling of Earth’s crust and upper-mantle suggests that ancient geologic events may have left deep ‘scars’ that can come to life to play a role in earthquakes, mountain formation, and other ongoing processes on our planet.

Mantle Plumes are columns of hot magma rising by convection in the mantle, believed to cause volcanic activity in hot spots, are often the source of mountain building such as the Hawaiian Islands, and are away from plate margins. This changes the widespread view that only interactions at the boundaries between continent-sized tectonic plates could be responsible for such events.

A team of researchers from the University of Toronto and the University of Aberdeen have created models indicating that former plate boundaries may stay hidden deep beneath the Earth’s surface. These multi-million-year-old structures, situated at sites away from existing plate boundaries, may trigger changes in the structure and properties at the surface in the interior regions of continents.

“This is a potentially major revision to the fundamental idea of plate tectonics,” says lead author Philip Heron, a postdoctoral fellow in Russell Pysklywec’s research group in UT’s Department of Earth Sciences. Their paper, “Lasting Mantle Scars Lead to Perennial Plate Tectonics,” appears in the June 10, 2016 edition of Nature Communications.

Heron and Pysklywec, together with University of Aberdeen geologist Randell Stephenson have even proposed a ‘perennial plate tectonic map’ of the Earth to help illustrate how ancient processes may have present-day implications.

“It’s based on the familiar global tectonic map that is taught starting in elementary school,” says Pysklywec, who is also chair of UT’s Department of Earth Sciences. “What our models redefine and show on the map are dormant, hidden, ancient plate boundaries that could also be enduring or “perennial” sites of past and active plate tectonic activity.”

To demonstrate the dominating effects that mantle plume anomalies below the Earth’s crust can have on shallow geological features, the researchers used UT’s SciNet – home to Canada’s most powerful computer and one of the most powerful in the world- to make numerical models of the crust and upper-mantle into which they could introduce these scar-like anomalies.

The team essentially created an evolving “virtual Earth” to explore how such geodynamic models develop under different conditions.

“For these sorts of simulations, you need to go to a pretty high-resolution to understand what’s going on beneath the surface,” says Heron. “We modeled 1,500 kilometers across and 600 kilometers deep, but some parts of these structures could be just two or three kilometers wide. It is important to accurately resolve the smaller-scale stresses and strains.”

Using these models, the team found that different parts of the mantle below the Earth’s crust may control the folding, breaking, or flowing of the Earth’s crust within plates – in the form of mountain-building and seismic activity – when under compression. In this way, the mantle structures dominate over shallower structures in the crust that had previously been seen as the main cause of such deformation within plates.

“The mantle is like the thermal engine of the planet and the crust is an eggshell above,” says Pysklywec. “We’re looking at the enigmatic and largely unexplored realm in the Earth where these two regions meet.”

“Most of the really big plate tectonic activity happens on the plate boundaries, like when India rammed into Asia to create the Himalayas or how the Atlantic opened to split North America from Europe,” says Heron. “But there are lots of things we couldn’t explain, like seismic activity and mountain-building away from plate boundaries in continent interiors.”

The research team believes their simulations show that these mantle anomalies are generated through ancient plate tectonic processes, such as the closing of ancient oceans, and can remain hidden at sites away from normal plate boundaries until reactivation generates tectonic folding, breaking, or flowing in plate interiors.

“Future exploration of what lies in the mantle beneath the crust may lead to further such discoveries on how our planet works, generating a greater understanding of how the past may affect our geologic future,” says Heron.

The research carries on the legacy of J. Tuzo Wilson, also a U of T scientist, and a legendary figure in geosciences who pioneered the idea of plate tectonics in the 1960’s.

“Plate tectonics is really the cornerstone of all geoscience,” says Pysklywec. “Ultimately, this information could even lead to ways to help better predict how and when earthquakes happen. It’s a key building block.”

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A new study in the April 22 edition of the journal ‘Science’, reveals that volcanic activity associated with the plate-tectonic movement of continents may be responsible for climatic shifts from hot to cold throughout much of Earth’s history. The study, led by researchers at The University of Texas at Austin Jackson School of Geosciences, addresses why Earth has fluctuated from periods when the planet was covered in ice to times when polar regions were ice-free.

Lead researcher Ryan McKenzie said the team found that periods when volcanoes along continental arcs were more active coincided with warmer trends over the past 720 million years. Conversely, periods when continental arc volcanoes were less active coincided with colder, or cooling trends.

For this study, researchers looked at the uranium-lead crystallization ages of the mineral zircon, which is largely created during continental volcanic arc activity. They looked at data for roughly 120,000 zircon grains from thousands of samples across the globe.

Zircon is often associated with mantle plumes. If the zircon Hf model age is very close to its formation age (zircon U–Pb) – the magma could be subsequent of a depleted mantle plume. On the other hand, if the zircon Hf model age is older than its formation age, it can be concluded that the magma was derived from enriched mantle sources or was contaminated by crustal materials.

“We’re looking at changes in zircon production on various continents throughout Earth’s history and seeing how the changes correspond with the various cooling and warming trends,” McKenzie said. “Ultimately, we find that during intervals of high zircon production we have warming trends, and as zircon production diminishes, we see a shift into our cooling trends.”

One question unanswered in recent climate change debates, is what caused the fluctuations in CO2 observed in the geologic record. Other theories have suggested that geological forces such as mountain building have, at different times in the planet’s history, introduced large amounts of new material to the Earth’s surface, and weathering of that material has drawn CO2 out of the atmosphere.

Using nearly 200 published studies and their own fieldwork and data, researchers created a global database to reconstruct the volcanic history of continental margins over the past 720 million years.

“We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years,” said co-author Brian Horton, a professor in the Jackson School’s Department of Geological Sciences. “The distinguishing part of our study is that we looked at a very long geologic record – 720 million years – through multiple warming and cooling trends.”

The cooling periods tended to correlate with the assembly of Earth’s supercontinents, which was a time of diminished continental volcanism, Horton said. The warming periods correlated with continental breakup, a time of enhanced continental volcanism.

As a living entity, Earth fights for its survival. If internal or external events begin to throw Earth out of balance i.e. orbital, tilt, or magnetic alignment – it begins to correct itself. When oceanic tectonic subductions occur, it cools the mantle and outer core. To balance this shift in temperatures, the Earth’s core increases heat and as a result releases what is known as “mantle plumes”. These plumes filled with super-heated liquid rock float up to the ocean bottom surface.

This action both cools the outer core and heats the oceans. As a result of heated oceans, we get tropical storms and various forms of extreme weather. When troughs, subduction zones, and rifts shift, as a result of convection, earthquakes, tsunamis, and volcanoes occur.

What makes this all work is the Earth’s magnetic field. Right now the magnetic field is weakening significantly. This will continue until it reaches zero point, at which time there will be a full magnetic reversal. Until this time, we will witness magnetic north bouncing in the northern hemisphere. Closer to the moments of a full reversal, we will see magnetic north drop down to/then below the equator.

As a result of a weakened magnetic field, larger amounts of radiation via charged particles such as solar flares, coronal mass ejections, gamma rays, and galactic cosmic rays – are more abundantly reaching Earth’s atmosphere and having a heightened reaction with Earth’s core layers. This is what causes looped reaction. Radiation heats the core layers, the outer core reacts by producing ‘mantle plumes’, which causes crustal fracturing, which then causes earthquakes, volcanoes, heated oceans – all of which cools the outer core.

This seemingly repeating loop will continue until the Earth will once again find its balance. Until then, we can expect naturally occurring earth changing events which will produce the loss of mass in some parts of the world, and emergence of mass in other parts. Maybe this is the time to change the things we can (attitude, environment, community, self, surroundings), one would be a fool not to apply themselves within their means – but then there is the time to loosen up a bit, know what is happening is just part of a process.

Just as the Earth, we humans can just keep on trucking, and maybe, just maybe, some will simply ‘enjoy-the-ride’.